A very high reaction enthalpy is an advantage of composite energetic formulations employing metallic fuels and solid oxidizers. However, the rates of reaction of such formulations are limited by condensed phase transport processes and are much lower than the reaction rates of mono-molecular energetic formulations, e.g., TNT, HMX, RDX, etc. Current research on composite energetics aims to reduce the length scales limiting mass transfer rates and to approach the reaction kinetics achievable for monomolecular formulations. Significant efforts have been made to produce metal fuel powders with nano-sized particles, see e.g., [D. P. Dufaux, R. L Axelbaum, Combustion and Flame 100 (1995) 350-358; L. J. Rosen, Z. Sun, R. L. Axelbaum, Chemical and Physical Processes in Combustion Combustion Institute, Raleigh, N.C., 1999, pp. 164-167]. Faster burning rates have been demonstrated with nano-sized metal powders for several applications, however difficulties in handling such powders and their incorporation into existing formulations have also been reported [P. Brousseau, J. C. Anderson, Propellants, Explosives, Pyrotechnics 27(5) (2002) 300-306]. To benefit fully from the small length scale and large specific surface of nano-sized metal particles, such particles should be intimately mixed with similarly sized oxidizer particles. Progress in this direction has been reported and nanopowders of metals and metal oxides have been mixed in organic solvents forming so-called Metastable Intermolecular Composites (MIC) [N. Bockmon, S. F. Son, B. W. Asay, J. R. Busse, J. T. Mang, P. D. Peterson, M. Pantoya, CPIA Publication 712 (38th JANNAF Combustion Subcommittee Meeting) (2002) 613-624]. Sol-gel processing has also been developed to produce nano-structured matrices of oxidizer materials that can be filled with metallic nano-sized fuels [T. M. Tillotson.; A. E. Gash, R. L. Simpson, L. W. Hrubesh, J. H. Satcher, J. F. Poco, Journal of Non-Crystalline Solids 285(1-3) (2001) 338-345].
In all of the current approaches, metal nanopowders have to be synthesized in a separate process and then mixed with the oxidizer. Handling of the highly reactive nano-sized fuel particles in close contact with oxidizer is needed and some passivation is always required. In order to reduce ignition sensitivity of metal nano-powders, protective coatings are used [D. Y Maeng, C. K Rhee, W. W. Kim, K. H Kim, Y. A. Kotov, Journal of Metastable and Nanocrystalline Materials 15-16 (2003) 491-494], which typically reduce the overall enthalpy of the fuel. Nano-sized ingredient powders also make it difficult to achieve the desired high density of the final energetic formulations. In addition, the costs of synthesis, passivation, and handling of the fuel and oxidizer nanopowders are currently prohibitively high.